There's Munzee, that uses QR codes stuck on items. I've never played it, but a buddy of mine loved it a couple years ago. I believe it had an active community at the time. It didn't interest me, so I can't comment further on it.

I grok the issue regarding socializing. I was doing some WU-GO last night, and ended up attacking a fortress with somebody, but couldn't find them while I was in a town plaza. They may have been parked in a car nearby, but it would be kind of creepy to walk over to someone sitting in a car at 11pm and ask them if they're playing the same game as you.